Combustion air vent control for furnaces

ABSTRACT

Various apparatus are disclosed for controlling the combustion air vent of fuel-fired furnaces. For a first embodiment of the invention, a furnace-controlled air valve is placed in the combustion air duct. When the furnace begins a heating cycle, the valve is opened. When the heating cycle ends, the valve is closed and remains closed until the beginning of the next heating cycle. For a second embodiment of the invention, a positive-displacement air pump is placed in the combustion air duct. The air pump pumps air from the exterior into the mechanical room at a controlled rate during each heating cycle of the furnace. The air valve or the air pump is controlled directly or indirectly by the furnace thermostat.

This application has a priority date based on the filing of Provisional Patent Application No. 60/765,821, titled COMBUSTION AIR VENT CONTROL FOR FURNACES, on Feb. 7, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to combustion furnaces and, more particularly, to the control of combustion air intakes for combustion furnaces having a combustion chamber that is not directly connected to the combustion air intake.

2. Description of the Prior Art

High-efficiency gas furnaces (those having efficiency ratings greater than 90 percent) typically have both a combustion air intake and a low-temperature exhaust vent, both of which are coupled directly to the combustion chamber of the furnace. As the combustion chamber is sealed from the room in which the furnace is installed, there can be little leakage of cold outside air into the room. Unfortunately, high-efficiency furnaces are not installed in the majority of new homes. Typically, they are installed in either new, high-end, custom homes or in existing homes by owners who are replacing an older furnace, and who intend to remain in those homes for a period sufficient to recover the additional cost required to purchase and install such furnaces. Most new homes constructed in this country are equipped with furnaces having efficiency ratings of around 80 percent. As homes have become increasingly airtight in an effort to minimize heat loss, building codes in effect in most states have evolved to require that a combustion air vent be provided between the exterior of the building and the mechanical room where the furnace is installed. In an airtight structure, a furnace will deplete the available oxygen and begin to produce carbon monoxide as combustion becomes increasingly incomplete. If the furnace exhaust vent is the only available conduit to the exterior, it is conceivable that the carbon monoxide would be drawn into the house as the furnace attempts to sustain the ongoing combustion of fuel. Because mechanical rooms are rarely well sealed from the rest of the house, combustion air vents can be a significant source of heat loss. This is particularly true when strong winds are blowing against the vent's exterior intake opening. In order to compensate for this heat loss, the furnace will use considerably more fuel than necessary to maintain a set temperature within the home. The effective efficiency of a furnace rated as being 80 percent efficient will be far less than 80 percent if it must compensate for an ongoing condition of significant heat loss. Another problem related to cold air entering the combustion air vent is that the dwelling's hot water heater is usually located in the same utility room or closet as the furnace. Even worse, the main water line may enter the dwelling in the utility room or closet. When outside temperatures drop significantly below freezing, the inlet water line of the water heater, the main water line, or both lines may freeze. This is not only annoying to the occupants, but likely to cause damage to the pipes—particularly if they are made of copper or brass.

What is needed is an inexpensive, safe, and reliable control for combustion air vents used with all types of combustion furnaces, which include gas-fired, oil-fired, corn-fired, wood-pellet-fired and coal-fired types which do not have the combustion air vent coupled directly to the furnace combustion chamber. The provision of such a control will greatly improve the effective efficiency of such furnaces by preventing leakage of cold air into the house through the combustion air vent.

SUMMARY OF THE INVENTION

The present invention provides an apparatus for controlling the vent used to supply combustion air to combustion furnaces. For a first embodiment of the invention, a furnace-controlled air valve is placed in the combustion air duct. Many types of valves can be used, including flapper valves, poppet valves, butterfly valves, ball valves, and inflatable balloon valves. When the furnace begins a heating cycle, the valve is opened. When the heating cycle ends, the valve is closed and remains closed until the beginning of the next heating cycle. A solenoid or electric motor may be used to control a flapper valve, a butterfly valve and a ball valve. When an electric motor is used, position sensors or timed pulses can be used to ensure that the valve is in the proper position at the beginning of each cycle. An inflatable balloon valve can be controlled with an air pump that inflates the balloon through a one-way valve so that leakage through the pump will not deflate the balloon. Air pump operation can be timed or it can be shut off with a pressure sensor. Deflation of the balloon during heating cycles can be accomplished by sending a pulse of sufficient length to a solenoid-controlled valve which will permit the pressured air within the balloon to escape.

A second embodiment of the invention employs a positive-displacement air pump, which is placed in the combustion air duct and prevents most back-flow leakage of air. Many types of positive-displacement pumps are known in the art, including plunger or piston pumps, circumferential-piston pumps (characterized by the use of a pair of counterrotating rotors driven by external timing gears), diaphragm and bellows pumps, external gear pumps, internal gear pumps, lobed pumps, sliding vane pumps, flexible-vane pumps, nutating pumps, and twin screw pumps. When a heating cycle begins, the air pump begins to pump air into the mechanical room at a controlled rate that provides oxygen in an amount equal to or slightly less than the rate at which oxygen is being consumed by the ongoing combustion process. When the heating ends, the air pump stops pumping air, and does not begin pumping air again until the next heating cycle. As a safety feature, a bypass valve is opened if the air pump does not function. The air valve or air pump can be controlled by a voltage generated by either the thermostat or by the furnace. As a safety feature, the air valve may be a normally open valve that is held in a closed position between heating cycles by an electromagnet operated by the control voltage generated either by the thermostat or gas furnace. Alternatively, a warning signal can be broadcast indicating an air valve or air pump malfunction so that corrective action may be taken. Regardless of the type of positive-displacement air pump used, it should, ideally, be manufacturable at low cost, reliable over a long period of usage, and capable of relatively quiet operation. Leaf shutter valve, disc valve

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway view of a home in which a combustion furnace has been installed in the mechanical room;

FIG. 2 is an elevational view of a combustion air vent having a flapper valve installed therein, with the valve operated by a solenoid;

FIG. 3 is an elevational view of a combustion air vent having a butterfly valve installed therein, with the valve operated by a solenoid;

FIG. 4 is an elevational view of a combustion air vent having a ball valve installed therein, with the valve operated by a solenoid and in its open position;

FIG. 5 is an elevational view of a combustion air vent having a ball valve installed therein, with the valve operated by a solenoid and in its closed position;

FIG. 6 is an elevational view of a combustion air vent having a ball valve installed therein, with the valve operated by an electric motor;

FIG. 7 is an elevational view of a combustion air vent having a balloon valve installed therein, with the valve controlled by an electric pump and a solenoid-actuated pressure-release valve;

FIG. 8 is a cross-sectional view through a flexible vane pump;

FIG. 9 is a cross-sectional view through a sliding vane pump;

FIG. 10 is a cross-sectional view through a lobe pump;

FIG. 11 is a cross-sectional view through an internal gear, or gerotor, pump;

FIG. 12 is a cross-sectional view through an external gear, or Roots-type, pump;

FIG. 13 is an electrical block diagram of the control circuit for the control valve of FIGS. 2, 3 4 or 6;

FIG. 14 is an electrical block diagram of the control circuit for the forced air pump of either FIGS. 8, 9, 10, 11 or 12; and

FIG. 15 is an electrical block diagram of a control circuit for the balloon control valve of FIG. 700.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in detail with reference to the attached drawing figures.

Referring now to FIG. 1, a cutaway view of a home 101 is shown, in which a combustion natural gas furnace 102 has been installed in the mechanical room 103. A wall 104 separates the mechanical room 103 from the rest of the house. A natural gas supply pipe 105 supplies natural gas to a meter 106. Natural gas is fed to the furnace 102 first through an exterior cut-off valve 107 and then through an interior cut-off valve 108 positioned near the furnace 102. An exhaust flue 109 transfers combustion products from the furnace 102 to outside the home 101. A vertical air duct 110 transports heated air from the furnace 102 to a horizontal air duct 111 in the ceiling, from which the heated air is expelled from various ceiling registers 112A, 112B, and 112C. A combustion air vent 113 provides combustion air from the exterior of the house to the mechanical room 103. The furnace 102 then pulls combustion air directly from the mechanical room 103. A grill 115 prevents the entry of insects and small animals into the mechanical room 103 through the combustion air vent 113. A combustion air controller 116 is shown as a box and can take the form of an electromagnetically controlled valve or a positive displacement air pump. Although a natural gas combustion furnace 102 is shown in FIG. 1, and the invention is depicted and described as being used in combination with such a furnace, it should be understood that the invention can applied to combustion air vents used with any type of fuel-fired furnace, regardless of the type of fuel which it uses.

Referring now to FIG. 2, a combustion air vent assembly 200 having a flapper control valve 202 installed thereon is shown. The vent 113, which passes through an exterior wall 114, terminates in the interior of the mechanical room 103 with a valve body 201 (a first embodiment of air controller 116). The valve body has an opening that is controlled by a normally-open valve 202 that is hinged to the valve body 201. A control rod 203 couples the valve 202 to a solenoid 204, which is pivotably mounted so that the control rod 203 does not bind within the electromagnet 204. Leads 205 provide power to the solenoid 204 during periods between heating cycles.

Referring now to FIG. 3, a combustion air vent assembly 300 having a butterfly valve 301 installed therein is shown. The butterfly valve 301 having an actuator lever 305 has replaced the flapper valve 202 of FIG. 2, with control of the butterfly valve 301 being handled by a solenoid 302, which is coupled to the actuator lever by a control rod 304. Leads 303 provide power to the solenoid 204 during periods between heating cycles. The butterfly valve 301 is shown in its open position. A mounting bracket 307 is secured to the wall 114 with an anchor bolt 308.

Referring now to FIG. 4, a combustion air vent assembly 400 having a ball valve 401 installed therein is shown. The ball valve 401 has replaced the butterfly valve 301 of FIG. 3, with control of the ball valve 401 still being handled by a solenoid 302 via control rod 304 and actuator lever 305. Leads 303 provide power to the solenoid 302 during periods between heating cycles. The ball valve 401 is shown in its open position.

Referring now to FIG. 5, the ball valve 401 of the combustion air vent assembly 400 of FIG. 4 is shown in the closed position, with the control rod 304 having been rotated 90 degrees by movement of the control rod 304 brought about by action of the solenoid 302.

Referring now to FIG. 6, a combustion air vent assembly 600 having a ball valve 601 controlled by an electric motor 602 is shown. Leads 603 provide power to electric motor in order to change the rotational position of the ball valve 601 at the beginning and end of each heating cycle. If electric motor 602 is powered by AC current, power to the leads 603 can be controlled using sensors which detect the position of the ball valve 601. On the other hand, if electric motor 602 is powered by DC current, the ball valve 601 can be equipped with limit stops so that it bidirectionally rotatable within a range of 90 degrees. Polarity of the DC current can be reversed to reverse rotational direction of the motor 602 and current detection can be employed to determine when the ball valve 601 has reached a limit stop.

Referring now to FIG. 7, a combustion air vent assembly 700 having an inflatable balloon valve is shown. A balloon 701 is inflated with an air pump 702 having power input leads 703 at the end of each heating cycle so that it expands to a size 701A that blocks the combustion air duct 201. Inflation is through a one-way valve 704 so that leakage through the pump 702 will not deflate the balloon once the pumping action as stopped. Full inflation of the balloon 701 to size 701A can be achieved either by timing the operation of the air pump 702 at the end of each heating cycle or by having a pressure sensor 705 with electrical input 706. The pressure sensor 705 senses the air pressure within the balloon 701 and shuts off the pump 702 when the optimum pressure is attained. Deflation of the balloon 701 during heating cycles can be accomplished by sending a pulse to a bleed valve 707 that is controlled by a solenoid 708 having input leads 709, the pulse being of sufficient duration to permit the pressured air within the balloon to escape. If the pump 702 has internal leakage when not pumping, the bleed valve 707 and the one-way valve 704 can be combined into a single unit so that deflation of the balloon 701 will occur through the pump 702. For an enhanced embodiment of the inflatable balloon valve, the balloon 701 can be either completely deflated or partially inflated to accommodate different airflow requirements. For example, if only a hot water heater is operating at a particular time, the air flow requirements will be less than if the furnace is operating or if both the hot water heater and the furnace are operating simultaneously.

Referring now to FIG. 8, a flexible vane pump 800 has a low pressure intake 801, a high-pressure outlet 802, a generally circular or ovoid chamber 803, and a impeller 804 that is mounted on a rotatable shaft 805 that is offset from the center of the chamber 803. The impeller 804 has flexible elastomeric vanes 806 which conform to the contour of the chamber 802, thereby creating a succession of chambers that expand on the inlet side and contract on the outlet side as the impeller 804 rotates in a counter-clockwise direction.

Referring now to FIG. 9, a sliding vane pump 900 has a low pressure intake 901, a high-pressure outlet 903, a generally circular chamber 902, and an impeller 904 having sliding vanes 905 that is mounted on a rotatable shaft 907 that is offset from the center of the chamber 902. As with the flexible vane pump 800, a succession of expanding and contracting chambers are created as the impeller rotates. In this case, there is no need to provide a spring beneath each vane, as gravity will cause the vanes 905 to extend from the recesses and block the backflow of air when the pump is stationary.

Referring now to FIG. 10, a lobe pump 1000 having a pump housing 1001 resembles a gear pump. Motion of the rotors 1004A and 1004B creates an expanding cavity 1006A on the inlet side 1002, a constant-volume cavity 1006B that carries fluid or gas to the outlet side 1003, and a contracting cavity 1006C that forces fluid or gas out. Rotors are typically driven by external timing gears (not shown) to avoid rotor contact in the fluid stream. Lobed pumps have relatively large displacement, so they are more efficient that gear pumps.

Referring now to FIG. 11, an internal gear or gerotor pump 1100 has a pump housing 1101, a low pressure intake 1102, a high-pressure outlet 1103, an outer gear 1104 which has 7 lobes which meshes with an inner gear 1105 which has 6 lobes, and a rotatable shaft 1106 on which the inner gear 1105 is mounted. Expanding and contracting chambers 1107 are formed by the simultaneous rotation of the outer gear 1104 and inner gear 1105.

Referring now to FIG. 12, an external gear or Roots-type forced air pump 1200 is another type of pump which may be installed in the combustion air vent 113. The combustion air vent 113 enters the intake port 1201 of the housing 1202 of pump 1200 and exits through exhaust port 1203 into the mechanical room 103. When the pump 1200 is inoperative, air from the combustion air vent 113 cannot flow through the pump. However, when the left and right impellers 1204L and 1204R are spinning in counterclockwise and clockwise directions, respectively, air flows between the spinning lobes 1205L and 1205R of the impellers 1204L and 1204R, respectively, and the housing walls 1206L and 1206R.

For any of the pumps 800, 900, 1000, 1100 or 1200, the pump is operated at a speed that pumps the amount of air required by the furnace 102 for complete combustion of fuel consumed. If a constant speed pump motor is used, impeller rotational speed can be adjusted by adjustable belt or gear drives. Alternatively, a variable speed motor can be used to set the desired rotational speed.

Referring now to FIG. 13, a circuit diagram 1300, for the controlling the valve-control electromagnet 204 of FIG. 2 or the valve-control electromagnet 302 of FIG. 3, FIG. 4, or FIG. 5 is shown. The input winding of step-down transformer T1 is coupled to the 110-120 volt alternating line current 1301. Output from transformer T1 is sent to a bridge rectifier B1. Output from bridge rectifier B1 is filtered by capacitor C1 and resistor R1 to provide low-ripple DC current, which is passed through a fuse F1 and resistor R2 en route to the both the channel input 1302 of P-channel IGFET P-Q1 and the power input of relay 1303. An output voltage VO from either a thermostat or the furnace gas valve control is applied to the gate 1304 of P-channel IGFET P-Q1 through capacitor C2, which protects IGFET P-Q1 from over-voltage conditions. When VO is at zero voltage, the channel of IGFET P-Q1 conducts, thereby energizing the coil 1305 of relay 1303, causing relay contacts 1306 to close, and sending current through the relay to activate the valve-control electromagnet 204/302. Alternatively, when VO goes high, the channel of IGFET P-Q1 stops conducting, thereby cutting off current to the coil 1305 of relay 1303, causing relay contacts 1306 to open, cutting off current through the relay, and thereby deactivating the valve-control electromagnet 204/302. A diode D1 protects IGFET P-Q1 from voltage surges which occur as the magnetic field of coil 1305 collapses when power to it is cut.

Referring now to FIG. 14, a circuit diagram 1400 for controlling the motors of the positive-displacement air pumps 800, 900, 1000, 1100 or 1200 is shown. The input winding of step-down transformer T1 is coupled to the 110-120 volt alternating line current 1301. Output from transformer T1 is sent to a bridge rectifier B1. Output from bridge rectifier B1 is filtered by capacitor C1 and resistor R1 to provide low-ripple DC current, which is passed through a fuse F1 and resistor R2 en route to the channel input 1401 of N-channel IGFET N-Q1. An output voltage VO from either a thermostat or the furnace fuel valve control is applied to the gate 1402 of N-channel IGFET N-Q1 through capacitor C2, which protects IGFET N-Q1 from over-voltage conditions. When VO is at a voltage greater than the threshold voltage of IGFET N-Q1, the channel of N-Q1 conducts, thereby energizing the coil 1305 of relay 1303, causing relay contacts 1306 to close, and sending AC current through the relay to turn on the drive motor 1403 of the positive displacement pumps 800, 900, 1000, 1100 or 1200. When VO is zero and below the threshold voltage for IGFET N-Q1, power to the drive motor is cut. A diode D1 protects IGFET N-Q1 from voltage surges which occur as the magnetic field of coil 1305 collapses when power to it is cut.

Referring now to FIG. 15, a circuit diagram 1500 for controlling the inflation of the balloon valve of the combustion air vent assembly 700 of FIG. 7 is shown. The input winding of step-down transformer T1 is coupled to the 110-120 volt alternating line current 1301. Output from transformer T1 is sent to a bridge rectifier B1. Output from bridge rectifier B1 is filtered by capacitor C1 and resistor R1 to provide low-ripple DC current, which is passed through a fuse F1 and resistor R2 en route to the channel inputs of P-channel IGFET Q-Q2 and N-channel IGFET N-Q2. An output voltage VO from either a thermostat or the furnace fuel valve control is applied to the gates of both P-channel IGFET P-Q2 and N-channel IGFET N-Q2 through capacitor C2, which protects IGFET P-Q2 and IGFET N-Q2 from over-voltage conditions. Between heating cycles, VO is at a voltage less than the threshold voltage of both IGFET P-Q2 and IGFET N-Q2, thereby rendering the channel of P-Q2 conductive and the channel of N-Q2 non-conductive and applying voltage to both the gate and channel input of IGFET N-Q3. The coil 1305 of relay 1303 is energized, causing relay contacts 1306 to close, and sending AC current through the relay 1303 to the motor of air pump 702. Pressurized air from the air pump 702 causes the balloon 701 to inflate and seal the combustion air duct 201 (see FIG. 7). When the optimum pressure for full inflation of the balloon 701 is sensed by pressure sensor 705, the pressure sensor 705 grounds the gate of IGFET N-Q3, thereby cutting off power to the motor of air pump 702.

Still referring to FIG. 15, when a heating cycle begins, VO is at a voltage greater than the threshold voltage of both IGFET P-Q2 and IGFET P-N2, thereby rendering the channel of P-Q2 non-conductive and the channel of N-Q2 conductive. Voltage passing through the channel of IGFET N-Q2 activates a timing circuit 1501 so that a pulse of measured duration is sent to the input lead 709 of the solenoid 708 of bleed valve 707, thereby fully deflating the balloon 701 and opening the combustion air duct 201. This condition remains unchanged until the heating cycle ends and the thermostat control signal VO once again goes low, causing reinflation of the balloon 701.

Although only several embodiments of the invention have been disclosed herein, it will be obvious to those having ordinary skill in the art that changes and modifications may be made thereto without departing from the spirit and scope of the invention as hereinafter claimed. For example, poppet valves, leaf valves (e.g., a durable version of a camera shutter), and disc valves should be considered within the scope of the present invention. In addition, any type of positive-displacement, including single and double-screw type pumps, should also be considered to be within the scope of the present invention. 

1. In combination with a fuel-burning furnace controlled by a thermostat, said furnace being installed in an enclosure located within a habitable structure and requiring a duct for admitting combustion air from outside the structure into the enclosure, a duct control device comprising: an apparatus having a first state which blocks the flow of combustion air through the duct and a second state which allows the flow of combustion air through the duct; and a control apparatus which establishes and maintains said first state during periods between furnace heating cycles and establishes and maintains said second state during furnace heating cycles.
 2. The combination of claim 1, wherein said apparatus is a valve having a movable control element which either closes the duct when in a first position corresponding to said first state or opens the duct when in a second position corresponding to said second state, said movable control element operating under the control of said thermostat.
 3. The combination of claim 2, wherein said valve is selected from the group consisting of balloon valves, flapper valves, ball valves, and butterfly valves.
 4. The combination of claim 2, wherein said movable control element is moved between said first and second positions by mechanical actuators selected from the group consisting of an electromagnet in combination with a spring, an electromagnet in combination with gravitational force, DC electric motors and AC electric motors.
 5. The combination of claim 1, wherein said apparatus is a positive-displacement pump which prevents combustion air from flowing through the duct when in said first state and pumps combustion air through the duct when in said second state.
 6. The combination of claim 5, wherein said positive-displacement pump is selected from the group consisting of sliding vane pumps, flexible vane pumps, external gear pumps, internal gear pumps, Roots-type pumps, and rotary lobe pumps.
 7. The combination of claim 5, wherein said positive-displacement pump is powered by electrical current that is controlled by a switch that, in turn, is controlled by said thermostat.
 8. The combination of claim 7, which further comprises a transistor to which is applied a control voltage corresponding to an output voltage from said furnace thermostat, and wherein a high level control voltage causes said transistor to transmit power to said switch, thereby turning it ON, and a low level control voltage causes said transistor to cut power to said switch, thereby turning it OFF.
 9. The combination of claim 5, wherein said positive-displacement pump is powered by an electric motor selected from the group consisting of DC and AC motors.
 10. In combination with a fuel burning heating device controlled by a thermostat, said heating device installed in an enclosure located within a habitable structure and requiring a duct for admitting combustion air from outside the structure into the enclosure, a duct control apparatus comprising: means for blocking the flow of combustion air through said duct during periods between furnace heating cycles; and means for allowing the flow of combustion air through said duct during furnace heating cycles.
 11. The combination of claim 10, wherein said means for blocking and said means for allowing is a valve having a movable control element which either closes the duct when in a first position or opens the duct when in a second position, said movable control element operating under the control of said thermostat.
 12. The combination of claim 11, wherein said valve is selected from the group consisting of balloon valves, flapper valves, ball valves, and butterfly valves.
 13. The combination of claim 11, wherein said movable control element is moved between said first and second positions by the combination of an electromagnet and a spring.
 14. The combination of claim 11, wherein said movable control element is moved between said first and second positions by the combination of an electromagnet and gravity.
 15. The combination of claim 11, wherein said movable control element is moved between said first and second positions by an electric motor selected from the group consisting of DC motors and AC motors.
 16. The combination of claim 10, wherein said means for blocking and said means for allowing is a positive-displacement pump which operates under the control of said thermostat.
 17. The combination of claim 13, wherein said positive-displacement pump is selected from the group consisting of vane pumps, flexible member pumps, external gear pumps, internal gear pumps, Roots-type pumps, and rotary lobe pumps.
 18. The combination of claim 13, wherein said positive-displacement pump is powered by an electric motor selected from the group consisting of DC and AC motors.
 19. The combination of claim 10, wherein said means for blocking and said means for allowing are directly controlled by electrical power passing through a switch that is controlled by a signal generated by said thermostat.
 20. The combination of claim 10, wherein said switch is selected from the group consisting of solenoids, bipolar junction transistors, junction field-effect transistors, and insulated-gate field effect transistors. 